Ability to add a server shutdown and restart schedule to the dashboard

[CmMesquita]

Implements the feature requested in #2005.

Changes

• Adds a scheduling interface in the dashboard preferences to configure server shutdown and restart times
• Allows users to define recurring schedules based on selected days and specific times
• Provides options to create, edit, enable/disable, and delete schedules
• Integrates with a backend scheduler (cron-like system) without requiring manual configuration

Notes

• Simplifies server management for users unfamiliar with cron jobs or command-line tools
• Includes validation to prevent conflicting or invalid schedules
• No impact on existing manual shutdown/restart functionality
• Security and permissions remain consistent with current authenticated flows